Angiotensin-converting enzyme inhibitors (ACEI) are widely used for the treatment of pediatric hypertension, and yet there have been very few prospective controlled studies reported. This protocol is part of a multicentric effort to establish a dose-response relationship for enalapril in children age 6 to 18. We will also investigate the safety and tolerability of enalapril in this group and we will define the response of surrogate markers for matrix metabolism o ACEI.